A Comparative Study of the Pattern Formation in the Drying Protein Droplets suspended in the <u>De</u>-ionized water

Pattern formation in drying bio-relevant systems continues to attract major attention of the researchers because of its medical applications. Here, an extensive description of drying evolution and the final patterns are presented, highlighting the concentration dependence (from 1 to 13 wt%) on two globular proteins, lysozyme (Lys) and bovine serum albumin (BSA) prepared in de-ionized water. The drying process starts with a constant contact radius mode and shifts to a mixed-mode where both contact radius and contact angle changes. The contact angle decreases monotonically, whereas, the contact radius exhibits two regimes: an initial linear, and a later non-linear regime. Unlike linear regime, the non-linear regime is faster for Lys droplets. This results in the formation of a `mound'-like structure and a new feature, a `dimple' is observed in this structure and found to be influenced by the initial concentration. The cracks which are only seen near the edge of BSA droplets, are spread throughout Lys droplets. In particular, Lys shows a hierarchy from delaminated to spiral cracks, and the spirals obey the well-known logarithmic equations. The mean crack spacing is found to be smaller than BSA droplets, and finally, these patterns are interpreted using a mechanical shear mechanism.